The present disclosure relates to a drive apparatus for an oil-pump motor and a drive control method for an oil-pump motor.
A vector-control-type sensor-less method for estimating a position of a rotor of a brushless motor based on an induced voltage of the motor calculated from a motor constant such as a current, a voltage, and a winding resistance has been known. Japanese Unexamined Patent Application Publication No. 2014-064385 (hereinafter referred to as Patent Literature 1) discloses a technique for a vector-control-type sensor-less method in which 180-degree energized sine-wave driving is performed for obtaining position information of a rotor based on an induced voltage in a high-speed range in which a rotation speed of a brushless motor is higher than a minimum motor rotation speed, and 120-degree energized rectangular-wave driving is performed in a low speed range in which the motor rotation speed is lower than the minimum motor rotation speed. Japanese Unexamined Patent Application Publication No. 2010-233301 (hereinafter referred to as Patent Literature 2) discloses a technique in which a control mode is changed so that a brushless motor is driven by performing open-loop control without using a sensor upon start-up of the motor (a starting mode), and the brushless motor is driven by performing current-feedback control (a current-control mode) after the start-up of the motor.
The present inventors have found the following problem. That is, recently, it has been studied how to apply a vector-control-type sensor-less method to driving of an oil-pump brushless motor (hereinafter also referred to as an “oil-pump brushless motor”) It has been desired that oil-pump brushless motors be used in low-speed operations as well as in high-speed operations. As described above, in the technique disclosed in Patent Literature 1, the motor driving mode is changed between when the brushless motor is rotating at a high speed and when it is rotating at a low speed. However, when the motor driving mode is changed as described above, its control tends to become complicated. A simpler control method has been desired for driving of oil-pump brushless motors. However, when the 180-degree energized sine-wave driving, which is performed to estimate the position of the rotor based on the induced voltage, is performed over the entire speed range, the accuracy for estimating the position of the rotor deteriorates in low-speed operations in which the induced voltage is low. Therefore, there is a possibility that the rotor may not be smoothly rotated in the low-speed operation.
Meanwhile, the technique disclosed in Patent Literature 2 can prevent the accuracy for estimating the rotor position from deteriorating in the low speed operation. However, when this technique is applied to driving of a relatively large-sized brushless motor such as an oil-pump brushless motor, there is a possibility that vibrations may occur due to a deformation of the rotor that is caused as the current is increased in the starting mode.
Other problems and novel features will be apparent from descriptions in this specification and the accompanying drawings.